The present invention relates generally to improved fill patterns for semiconductor devices, and more particularly to geometrically simple arrays of fill patterns interspersed among conductive elements to promote the formation of an insulating planarization layer.
The deposition of the numerous layers is one of the key steps in the fabrication of semiconductor devices, where typically alternating patterns of conductive and nonconductive materials are topographically formed on a semiconductor substrate. In a typical photolithographic process, a patterned reticle is employed to provide masking of selected sections of a resist layer on both the semiconductor substrate and subsequent layers, repeated through numerous steps to build a three-dimensional network of connectors. However, the addition of multiple layers causes the topographic projection to become more and more nonplanar; these surface undulations can lead to a loss of resolution in the lithographic masking process.
It is therefore highly desirable from a process and quality control perspective to have as little surface undulation as possible on the built-up semiconductor device. One way to minimize the surface undulation is to planarize each exposed surface with one or more insulative layers using known procedures, such as spin-on glass (SOG) or chemical vapor deposition (CVD) methods. One commonly used material in this CVD process is tetraethylorthosilicate (TEOS). When either of these approaches are used to deposit a layer over large tracts of non built-up area, they tend to produce tapered layer thickness variations near the topographic regions in a manner similar to that of a meniscus formed near a container wall due to surface tension in a liquid. To achieve the desired level of planarization, it is precisely this conformal behavior, prevalent in wide-open areas, that substrate designers have been trying to avoid. Similarly, when spacing widths between the rigid upstanding structures varies, the aforementioned layer fill techniques are less than wholly effective at achieving the desired planarization, as spaces of varying size permit disparate amounts of SOG or TEOS to flow into them, and at different rates.
Additional methods have been employed to improve the planarity of insulative layers. One well-known approach involves the placement of xe2x80x9cdummyxe2x80x9d or fill patterns in between the topographic conductive elements to reduce the incidence of conformal dips in the insulative layer. The presence of these fill patterns which, by interrupting otherwise large tracts of unsupported fill area, subdivide and create smaller valley- or grid-like regions for SOG or TEOS layers to fill. However, the addition of fill patterns adds complexity, as additional steps must be included to ensure their mechanical and electrical compatibility. For example, since many fill patterns are metal (often deposited simultaneously with the conductive element steps), they can be a source of unwanted conductivity or capacitance. Similarly, a lack of uniformity of spacing between the patterns making up the fill pattern array hampers the even distribution of the layers. The relatively non-uniform spacing between adjacent topographic structures also militates against lower processing costs, where these considerations dictate that fill patterns and the arrays made therefrom be as simple as possible. The cost of depositing customized, non-uniform fill patterns can have a significant impact on fabrication cost; on the other hand, improper attention to a grid or valley layout between fill patterns can lead to spaces that, if inclusive of long straight paths and high throughflow intersections, will exhibit uneven planarization layer flow, and subsequent undulated layer deposition. Accordingly, fill pattern size and spacing become critical design considerations to the person responsible for the circuit layout.
Accordingly, the need exists for devices in which fill patterns can be consistently and substantially planar across the entire region of the upper surface of the semiconductor device to provide inexpensive, compact and reliable structures.
The present invention satisfies the aforementioned need by providing a planarized semiconductor device and a system which utilizes a reticle configuration that promotes the formation of a planarized landscape on the surface of a semiconductor device. The various layers, regions, and structures of the embodiments of the device according to the present invention may be formed by utilizing conventional semiconductor device fabrication techniques. The selection of these specific techniques may vary from application to application and, with the exception of the fabrication steps outlined herein, is not the subject of the present invention.
According to an aspect of the present invention, a method of fabricating a semiconductor device is disclosed, where the steps include: providing a generally planar semiconductor wafer substrate made up of substantially orthogonal first and second in-plane dimensions; defining a topographic layer of conductive lead line material such that it comprises at least first and second sides that extend coplanar with the wafer substrate; depositing one or more topographic layers of conductive lead line material on the substrate; depositing a plurality of topographic fill patterns adjacent either the conductive lead line material or another fill pattern such that spaces defined between the topographic structures possess substantially equal width as any other space; arranging the topographic fill patterns and the topographic layers of conductive lead line material so that a grid defined by a plurality of crossings of the spaces contains no linear dimension longer than the longest dimension of any one of the topographic fill patterns, and that no intersection defined by any of the plurality of crossings includes uninterrupted linear dimensions. An additional step includes depositing a planarization layer over the substrate such that it fills up the grid pattern, laterally surrounding the topographic structures of conductive lead line material and fill patterns.
Optionally, the step of depositing the insulative layer includes depositing either a layer of spin-on glass or TEOS. In addition, the deposition of the insulative layer produces a top surface substantially co-planar with a top surface of the layers of conductive lead line material and the fill patterns. An additional step may include defining an array comprising at least one of the fill patterns and conductive lead line layers such that no portion of any of the fill patterns overhang the array boundary. The array can be thought of as containing numerous topographic structures repeated in a fairly regular geometric pattern such that it takes on a relatively uniform appearance. One way to achieve a regular geometric pattern is to have the periphery of the array be mostly bounded by the straight-edged sides of the fill patterns.
According to another aspect of the present invention, a semiconductor is disclosed. The semiconductor includes a substantially planar substrate with first and second topographic patterns, or structures, defined by active lead lines and dummy fills (both also referred to as peaks), respectively deposited on the substrate. A repeating array, which itself includes a substantially planar grid comprising a plurality of interconnected valleys circumscribing the first and second topographic patterns, is disposed over the substrate, and is configured such that the array periphery is substantially bounded by straight edges of the dummy fills, active lead lines, or combination of both. Furthermore, no portion of any of the dummy fills extends laterally beyond the periphery. Within the grid, the longest linear dimension of each of the valleys is no longer than the longest lateral dimension of any of the dummy fills, and no intersection defined by a crossing between any two valleys includes uninterrupted linear dimensions. In the alternate, a plurality of first and second topographic structures deposited over planar substrate, where the first are conductive lead lines, and the second are fill/dummy patterns, both including top surfaces thereon that are generally co-planar with one another. In addition, a planarization layer deposited over the substantially planar substrate such that it is disposed at least within the gridded valley and laterally surrounds the first and second topographic structures.
Optionally, the semiconductor further may include a substantially planar layer of insulative material deposited over the valleys, and has a thickness selected to render a top surface of the substantially planar layer substantially co-planar with a top surface of the peaks. In addition, the semiconductor device further includes a lateral dimension defining a width of any one of the interpeak spaces such that it is substantially as wide as all other interpeak spaces. This ensures a relatively constant spacing between adjacent peaks, whether the peaks be topographic conductive lead lines or topographic dummy patterns. Additionally, the insulative material on the semiconductor is an oxide-based ceramic.
In still another aspect of the present invention, a memory cell is disclosed. The device includes, in addition to the semiconductor configuration of the previous embodiment, a switching device (such as a transistor) and a charge storage device (such as a capacitor) in electrical communication with the switching device. The substrate defines first and second orthogonal in-plane dimensions. The first topographic structures are made up of conductive lead lines in electrical communication with the switching device. The second topographic structures include a top surface generally co-planar with the top surfaces of the first topographic structures. The gridded valley is made up of a first set of interconnected series of spaces that extend in the first orthogonal in-plane dimension, and a second set of interconnected series of spaces that extend in the second orthogonal in-plane dimension.
Optionally, the memory cell includes a width of each of the interconnected series of spaces that is between 0.25 and 0.5 micron, and the second topographic structures define first and second in-plane dimensions extending in first and second orthogonal in-plane dimensions. At least one of the fill patterns may overlap with at least one adjacent fill pattern along at least one of the first and second in-plane dimensions. Also, the second topographic structures may be any of a variety of geometric shapes. Additionally, the first and second topographic structures may be made of the same material.
In still another aspect of the invention, a reticle,used to make a memory cell is disclosed. The reticle comprises a surface into which plurality of lead line cutouts and a plurality of fill pattern cutouts are made. The cutouts are adapted to define topographic peaks on the surface of a semiconductor, where the lead line cutouts are shaped to further define at least one lead line, and the fill pattern cutouts define a plurality of dummy patterns spaced apart from one another. The fill pattern cutouts are interspersed between the lead line cutouts, and are spaced apart from each of the lead line cutouts by an amount sufficient to avoid capacitive communication between a metal lead line and a metal fill pattern formed on a memory cell by the reticle. The lead line and fill pattern cutouts are disposed in an array within a surface of the reticle such that the periphery of the array is substantially bounded by straight edges, and that no portion of any of the fill pattern cutouts within the array extends laterally beyond the periphery. A grid, which is part of the reticle surface remaining after the fill pattern and lead line cutouts have been created, includes an interconnected series of spaces between adjacent cutouts. A lateral distance defining a width of any one of the series of spaces is substantially equal to that of any other of the series of spaces within the grid, while the longest linear dimension between each of the series of spaces is no longer than the longest dimension of any of the fill pattern cutouts. Furthermore, no intersection defined by a crossing between any two of the interconnected series of spaces includes uninterrupted linear dimensions.
Optionally, the fill pattern cutouts are any of a variety of geometric shapes. In addition, at least one of the fill pattern cutouts further define a first in-plane dimension and a second in-plane dimension substantially orthogonal to the first in-plane dimension such that at least one of the fill pattern cutouts overlaps with at least one adjacent fill pattern cutout along at least one of the first or second in-plane dimensions. Also, a lateral dimension defining a width of any one of the interconnected series of spaces is substantially the same between all other the series of spaces.
In yet another aspect of the invention, a semiconductor fabrication system is disclosed. The semiconductor fabrication system includes: a photoresist application mechanism to deposit photoresist onto a semiconductor substrate; an electromagnetic radiation source to illuminate at least a portion of the photoresist; a solvent dispensing mechanism to wash away unexposed photoresist; an etching mechanism to selectively remove at least one layer of insulative coating; and a reticle with a generally planar body similar to that of the previous embodiment.
In yet another aspect of the present invention, a motherboard assembly employing memory cells is disclosed. The motherboard includes a generally planar board, a plurality of interconnect devices to provide electrical communication between the motherboard and various input, output and memory devices, and mounts for a microprocessor, plurality of memory devices and plurality of controller sets, all of which are mounted to the generally planar board. The motherboard also includes at least one semiconductor mounted to the generally planar board, where the semiconductor is from the group consisting of the microprocessors, memory devices and controllers. The semiconductor is similar to that of the previously discussed embodiments.
In yet another aspect of the present invention, a computer system employing memory cells is disclosed. The computer system includes a microprocessor, at least one input electrically coupled to the microprocessor, a mass storage unit electrically coupled to the microprocessor, an output electrically coupled to the microprocessor and at least one memory device adapted to store computer programs for use by the microprocessor such that it is electrically coupled to the microprocessor. The memory device is similar to that of the previously discussed embodiments.
In still another aspect of the present invention, a method of fabricating a reticle is disclosed, the method including the steps of producing a plurality of lead line cutouts in a reticle body; producing a plurality of fill pattern cutouts interspersed between the plurality lead line cutouts, and forming a grid comprising an interconnected series of spaces. The structure of the reticle is similar to that of the previous reticle embodiment.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.